One attractive approach for removal of small particles in cleaning processes, such as semiconductor wafer and chip processing, is use of acoustic cavitation in liquids, whereby voids or cavities are created in a liquid and subsequently caused to implode, to undergo micro-acoustic streaming, or to otherwise transfer energy from a cavity to one or more particles adjacent to the (former) cavity. If these (unwanted) particles are located on and temporarily attached to an adjacent surface, such as a semiconductor wafer or chip, these particles can be removed by the force of a collapsing cavity or by micro-acoustic streaming. The frequencies used to induce cavitation in a liquid are often of the order of 1 MHz, and the corresponding cavitation systems are sometimes referred to as megasonic systems.
However, two problems associated with use of cavitation for particle removal with the systems available today are (i) the inhomogeneity of the sizes and density of the cavities or voids created, before collapse occurs, and (ii) the resulting non-uniformity in local particle removal. What is needed are systems and methods that provide and maintain reasonable homogeneity in acoustic cavitation density and that allow a representative cavitation density to be varied according to the nature of the particles to be removed from a surface.